JPH0678271B2 - Method for producing silver oxalate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing silver oxalate. More specifically, it relates to a method for producing silver oxalate having a large grain size.

<Prior Art> As is well known in the art, a water-insoluble oxalate salt is produced by adding oxalic acid or a water-soluble oxalate salt to a silver salt such as silver nitrate in an aqueous solution.

A silver-supported catalyst is used as a reaction catalyst for producing ethylene oxide by vapor-phase oxidation of ethylene, and silver oxalate is used as a raw material for preparing the silver-supported catalyst.

JP-B-55-11895, JP-B-58-1629 and JP-A-52
-82691 discloses a method for producing a silver-supported catalyst for the production of ethylene oxide by vapor-phase oxidation of ethylene, wherein oxalic acid and / or a water-soluble oxalate is added to a silver salt such as silver nitrate in an aqueous solution to give water. An insoluble silver oxalate precipitate is formed, and after it is washed with water and a complexing agent such as an amine and water are mainly added to dissolve it as a silver complex salt, which is impregnated in a porous refractory carrier, and then heat treated to form a silver complex salt. Disassemble the
A method of depositing silver on a carrier is disclosed.

Among them, in Example 1 of JP-B-58-1629, 6 g of anhydrous silver nitrate and 3.3 g of potassium oxalate were separately dissolved in 100 ml of water, and the solutions were mixed and heated in a steam bath to produce The resulting silver oxalate precipitate was centrifuged to remove the liquid on the surface by decantation, and the precipitate was removed with hot distilled water at 60-90 ° C.
It is described that the cells were washed 5 times with 0 ml, and each time they were washed, they were subjected to centrifugation to remove water by decanting.

As can be understood that the produced silver oxalate precipitate is separated by centrifugation, the silver oxalate precipitate obtained by simply mixing and heating the silver nitrate aqueous solution and the potassium oxalate aqueous solution as described above has fine particles. It has a high water content and is a sticky sticky precipitate. For this reason, the precipitation has the following disadvantages: 1) Poor sedimentation, 2) Poor performance when attempting to separate by filtration, requiring a special filter, labor is required, and 3) Water washing takes time. .
When this precipitate is used for preparing a catalyst for ethylene oxide production, the precipitate adheres to a container, cloth, or the like, or is used as a carrier for the next step (preparation of silver complex salt), or input for preparing complex salt. It also adheres to equipment and the like, leading to loss of expensive silver and time-consuming, which causes disadvantages in catalyst production.

<Problems to be Solved by the Invention> Therefore, an object of the present invention is to provide a novel industrially advantageous method for producing silver oxalate.

Another object of the present invention is to provide a method for producing silver oxalate, which is extremely excellent in sedimentation property, transitory property and water washability.

Yet another object of the present invention relates to a method for producing surprisingly large particle, low water content, dry, non-sticky and easy to handle oxalic acid precipitates.

Still another object of the present invention is to prepare a catalyst for an oxidation reaction in producing ethylene oxide from ethylene,
The present invention relates to a method for producing silver oxalate, in which the complexing step of reacting with an amine and dissolving is completed rather than fine silver oxalate, and therefore can be very advantageously used for preparing the catalyst.

Further objects and advantages of the present invention will be apparent from the following description.

<Means and Actions for Solving Problems> According to the present invention, the above objects and advantages of the present invention are that a silver salt as a reaction raw material and oxalic acid and / or an oxalic acid salt are mixed in an aqueous medium at pH 5 It is achieved by a method for producing silver oxalate, which is characterized by reacting while maintaining the temperature below to form a precipitate of silver oxalate.

The silver oxalate precipitate produced according to the present invention has a much higher settling rate and overspeed than the silver oxalate precipitate produced by the conventional method, as will be shown in the examples described later. The silver oxalate precipitate produced by the present invention usually has an average particle size of about 2 to 3 μm or less, whereas the silver oxalate precipitate produced by the conventional method usually has an average particle size of about 4 to 4.
It has a very large average particle size of 20 μm.

It goes without saying that both the silver salt and the oxalate salt used as starting materials in the present invention are different compounds from the reaction product silver oxalate. As such a silver salt, for example, silver nitrate, silver oxide, silver lactate or the like is used. Of these, silver nitrate has a high solubility, and therefore is preferably used rather than water-insoluble or sparingly soluble silver oxide, silver lactate, and the like.

As the oxalate salt, for example, sodium oxalate, ammonium oxalate, potassium oxalate and the like are used. Of these, potassium oxalate is particularly preferred.

Particularly, it is most preferable to use a combination of silver nitrate and potassium oxalate because they are easily available and easily handled.

In the method of the present invention, the starting materials as described above are mixed in an aqueous medium at pH 5
It is carried out by maintaining the reaction below. The pH during the reaction is preferably 1 to 4.

Both inorganic and organic acids can be used to adjust the pH, but avoid the use of acids which react to form insoluble silver salts, such as hydrochloric acid which reacts to form water insoluble silver oxide. That's all. Nitric acid is most preferably used as the acid for adjusting the pH.

The reaction is usually carried out at a temperature in the range of 0 ° to 80 ° C, more preferably at a temperature in the range of 40 ° to 60 ° C. When carried out at such a temperature, a silver oxalate precipitate having a relatively large particle size can be formed, and the precipitation of the formed precipitate can be accelerated. Reaction temperatures above 80 ° C are not desirable because the silver oxalate formed tends to become colored due to thermal decomposition and the like. The temperature in the system after the formation of the precipitate is substantially complete is not very important.

In the method of the present invention, preferably, an aqueous solution of a silver salt as a raw material and an aqueous solution of oxalic acid and / or an oxalic acid salt are separately prepared, and either one of the aqueous solutions is added and mixed with the other, or both aqueous solutions Can be advantageously carried out by introducing into a separate reaction vessel and mixing in the reactor.
Of these, the last method of introducing both aqueous solutions into separate reaction vessels is most preferred. At that time, a method may be adopted in which acidic water having a pH of 5 or less is previously present in the reaction solution, and the above-mentioned both aqueous solutions are added thereto. Further, in any of the above embodiments, it is desirable that the pH of one or both aqueous solutions is adjusted to 5 or less, preferably 1 to 4 before mixing.

In addition, both of the above aqueous solutions before mixing the raw materials are 0.1 to 6
It is preferable that the concentration is within the specified range. More preferably, the normalities of both aqueous solutions to be mixed are made substantially equal within the above concentration.

The present invention will be further described by the above most preferred embodiment. The addition rate of both aqueous solutions is determined in consideration of the relationship between the stirring conditions and the liquid concentration, but basically both liquids have the same normality. It is important to add and stir at the addition rate so as not to cause a large concentration non-uniformity in the liquid or a pH difference. Even partially, the pH of the liquid is 5
Must not exceed. It is preferable that the addition of both aqueous solutions be completed in about 1 hour, depending on the reaction scale.

In the method of the present invention, stirring is important for eliminating the non-uniformity of the concentration in the liquid as described above, to eliminate the pH more than as much as possible, and to obtain complete mixing, and about 10 to 500 rpm is suitable for practical use. . However, after the addition of both solutions is completed and the precipitation is completed, the presence or absence of stirring is not so important.

As can be understood from the above description, the method of the present invention comprises: an aqueous solution of silver nitrate whose pH is adjusted to 1 to 4 in water whose pH is adjusted to 1 to 4 by nitric acid; and potassium oxalate whose normality is almost the same. It is advantageously carried out by the method of adding at about the same rate as the aqueous solution (pH not adjusted) under good stirring conditions.

Although the method of the present invention is preferably carried out in the range of pH 1 to 4 as described above, after the reaction is substantially completed, that is, after the silver oxalate is substantially precipitated,
A pH of 4 or above is desirable. Thus, even after the reaction is substantially completed, the slightly dissolved silver ions in the reaction solution can be recovered. Therefore, it is advisable to add a small amount of alkali such as NaOH, or to add an excess of potassium oxalate (5% to 10%) to the equivalent amount.

<Examples> The present invention is described below with reference to Examples.

The characteristic values in Tables 1 and 2 showing the properties of silver oxalate precipitate are defined as follows.

1) Moisture content: Proportion (% by weight) of water contained in the silver oxalate cake after washing with water.

2) Precipitation volume: Ratio (volume%) of the precipitation volume to the total volume of the mother liquor containing the precipitate, which was sufficiently left to stand after completion of the precipitation adjustment.

3) Overspeed: The final overspeed when passing through a nutche having an appropriate diameter selected so that the final cake thickness becomes the same according to the amount of precipitation, but the paper is ToYo No2, and the degree of vacuum is 560 Torr.

4) Amount of washing water: Conductivity of liquid is 50μ / cm or less
The required amount of cake washing water per unit of silver oxalate precipitate
It is shown.

5) Crystal particle diameter: average particle diameter of crystal particles constituting silver oxalate precipitate, determined by a scanning electron microscope.

6) Final mother liquor pH: pH of the mother liquor after the completion of precipitation.

1) is a measure of ease of handling such as stickiness of precipitation.

3) and 4) serve as a measure of the precipitation precipitation.

2) and 5) are a scale showing the size of the precipitated crystal particles.

6) is a scale showing the amount of dissolved silver in the mother liquor. As shown in FIG. 2, if the pH is 4 or more, the problem of loss due to dissolved silver does not occur.

Example 1 pH 2.6 nitric acid aqueous solution of 13 containing 1.7 g of AgNO ₃ (1.4
(Normal concentration) was prepared and heated to 60 ° C. Then K ₂ C ₂
An unadjusted pH (pH 8.6) 14.3 potassium oxalate aqueous solution (1.4 normal concentration) containing 1844.7 g of O ₄ · H ₂ O was prepared, and this was heated to 60 ° C. Further adjust the pH to 2.5 with nitric acid,
A mixing tank filled with water of 4.3 heated to 0 ° C. was prepared. This water-stirred mixing tank was stirred, and the previously prepared silver nitrate aqueous solution and potassium oxalate aqueous solution were simultaneously fed into the mixing tank from the opposite direction of about 180 degrees at the same supply rate of 13 / h. That is, silver nitrate and potassium oxalate were added in approximately equal regular amounts to prepare a silver oxalate precipitate. Therefore, the silver nitrate aqueous solution required about 60 minutes, and the potassium oxalate aqueous solution required about 66 minutes to supply the total amount. The formation of the silver oxalate precipitate was completed in about 60 minutes, and in the remaining 6 minutes, a stoichiometric amount of excess potassium oxalate aqueous solution was added, thereby increasing the pH in the mixing tank. The change in pH in the mixing tank at this time is shown in FIG. 1 attached. During the liquid supply, the stirring in the mixing tank was sufficiently performed, and the temperature of each liquid was maintained at about 60 ° C. until the addition was completed. After the preparation of the precipitate, the precipitate was depressurized and washed with water. The conductivity of the rinsing water is 50 μ / c
Washing with water was stopped when the water was less than m. The properties of the silver oxalate precipitate thus obtained are shown in Table 1.

Example 2 The temperatures of the silver nitrate aqueous solution, the potassium oxalate aqueous solution, and the water in the mixing tank were all about 40 ° C., and the water in the mixing tank was
The same procedure as in Example 1 was repeated except that the pH was changed to 2 (before mixing). The properties of the obtained precipitate are shown in Table 1.

Example 3 The temperature of the silver nitrate aqueous solution, the potassium oxalate aqueous solution, and the water in the mixing tank were all set to about 20 ° C. and the pH of the water in the mixing tank was adjusted.
The same procedure as in Example 1 was performed except that No. 2 was set (before mixing). The properties of the obtained precipitate are shown in Table 1.

Example 4 The temperature of the silver nitrate aqueous solution was set to about 20 ° C., and the temperature of the potassium oxalate aqueous solution and the water in the mixing tank were set to about 60 ° C. In addition, the pH of the water in the mixing tank was set to 2 (before mixing), and the temperature of the potassium oxalate aqueous solution and the mixing tank were not maintained (thus, the temperature of the mixing tank changed depending on the progress, and when the precipitation preparation was completed). The temperature was 40 ° C). The same procedure as in Example 1 was carried out except that the above changes were made. The properties of the obtained precipitate are shown in Table 1.

Example 5 Example 5 was repeated except that the pH of the aqueous silver nitrate solution and the water in the mixing tank were adjusted to 4. The properties of the obtained precipitate are shown in Table 1.

Comparative Example 1 The same procedure as in Example 1 was performed except that the pH of the silver nitrate aqueous solution and the water in the mixing tank were not adjusted (silver nitrate solution pH 5.3, water in the mixing tank was not added with acid). The properties of the obtained precipitate are shown in Table 2.

Comparative Example 2 13 silver nitrate aqueous solution (1.4 normal concentration) containing 3091.7 g of AgNo ₃ was heated to about 60 ° C. without adjusting the pH (pH 5.3).
To this, 13 l of a pH-adjusted potassium oxalate aqueous solution (pH 8.6, 1.54 normal concentration) in which 1844.7 g of K ₂ C ₂ O ₄ · H ₂ O was dissolved is kept at about 60 ° C and stirred for about 30 Add over minutes and thus prepare a silver oxalate precipitate. Subsequent operations were the same as in Example 1, and washing with water was performed. The properties of the precipitate thus obtained are shown in Table 2.

Example 6 Silver oxalate silver cake 12 prepared in Example 4 and having a water content of 14.1% 12
9.3 g (78.9 g as silver) was taken and added to an amine aqueous solution consisting of 39.5 g of ethylenediamine, 10.8 g of 1,3 diaminopropane and 50.0 g of water to prepare a silver oxalate-amine complex solution. The solution was sufficiently stirred, and the addition rate was controlled so that the solution temperature did not exceed 35 ° C due to the heat of complexation.
The silver oxalate precipitate was well dispersed in the amine aqueous solution, and the complexation reaction proceeded easily. The time required to complete the preparation of the complex solution was 37 minutes.

Comparative Example 3 Silver oxalate cake 13 having a water content of 20.0% prepared in Comparative Example 13
8.9g (78.9g as silver, same as the amount of silver used in Example 6)
A silver oxalate-amine complex solution was prepared in the same manner as in Example 6 except that was used. The silver oxalate precipitate adhered to the lower part of the complexing vessel in a lump form and the complexing reaction was difficult to proceed. The time required to complete the preparation of the complex solution was 84 minutes.

<Effects of the Invention> As described above, according to the present invention, it is possible to produce a silver oxalate precipitate which is larger and smoother than particles produced by the conventional method. That is, since the produced silver oxalate has large particles and is smooth, it is easy to settle the particles in the super-water washing step, pass the particles, and wash the particles with water in the complexing step during the next catalyst preparation. Since it has good dispersibility in the interior, it has the advantage that the complexation is fast and the precipitate is easy to handle and transport because it has no adhesion.

[Brief description of drawings]

FIG. 1 shows the fluctuation of pH in the reaction mixing tank when silver oxalate is produced according to the present invention. FIG. 2 shows the solubility dependence of silver oxalate with pH.

Claims (11)

[Claims] 1. A silver oxalate precipitate is produced by reacting a silver salt as a reaction raw material with oxalic acid and / or oxalate in an aqueous medium while maintaining a pH of 5 or less. Method of producing silver oxalate. 2. A process according to claim 1 in which the reaction is carried out at a temperature in the range 0 to 80 ° C. 3. The method according to claim 1, wherein the reaction is carried out at a pH of 4 or less. 4. The method according to claim 1, wherein the reaction is carried out at a pH of 4 or less, and after the silver oxalate is substantially precipitated, the pH of the reaction system is set to a value higher than 4. . 5. The method according to claim 1, wherein the starting oxalate is potassium oxalate. 6. The method according to claim 1, wherein the raw material silver salt is silver nitrate. 7. The method according to claim 1, wherein the pH adjuster for adjusting the pH to 5 or less is nitric acid. 8. The method according to claim 1, wherein the raw material silver salt and the oxalic acid and / or oxalate are prepared in the form of an aqueous solution before being mixed. 9. The method according to claim 8, wherein the concentration of the raw material silver salt aqueous solution is in the range of 0.1 to 6 N. 10. The method according to claim 8, wherein the concentration of the aqueous solution of oxalic acid and / or oxalate as a raw material is in the range of 0.1 to 6 N. 11. An aqueous silver nitrate solution having a pH of 1 to 4 and an aqueous potassium oxalate solution having a pH of approximately 1 to 4 in stirred water having a pH of 1 to 4 at approximately the same rate. The method according to claim 1, wherein the pH is raised to 4 or more by further adding an aqueous potassium oxalate solution in excess of the equivalent amount after completion of the addition of both solutions.